QUALITY HEAVY DUTY PARTSPage 10

AIR BRAKE SYSTEM TROUBLESHOOTING

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Page 11QUALITY HEAVY DUTY PARTS

AIR BRAKE SYSTEM TROUBLESHOOTING

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QUALITY HEAVY DUTY PARTSPage 12

AIR BRAKE SYSTEM TROUBLESHOOTING1.) Before replacing any valve with a new or remanufactured valve, be sure to blow the air lines out eitherusing the vehicle’s own air supply or shop air. Dirt is the greatest cause of premature air valve failure.

2.) If pipe dope is used on fittings, use it sparingly. This can also get into the unit and cause a failure.

3.) When installing fittings into a remanufactured valve, do not over tighten or it will crack the casting.

4.) With the introduction of spring brakes, anti-compounding and 121 air brake systems, because a valve isleaking air out of its exhaust, does not mean the valve is at fault. If a spring brake is leaking from the thespring brake to the service brake side, that air will travel back up the service line and out the exhaust of thenext valve back. Before replacing a valve that has air leaking from its exhaust, disconnect the delivery linesfrom that valve to determine if air is being fed back from some other valve or unit.

TRUCKS, TRACTORS and BUSES1.) Insufficient Brakes-Brakes need adjusting, lubricating or relining.-Low air pressure in the brake system (below 60psi).-Brake valve delivery pressure below normal.-Wrong size actuators and/or slack adjusters.-Failure of part of a dual air system.-If remote mounted brake valve, check linkage.

2.) Brakes Apply Too Slowly-Brakes need adjusting or lubricating.-Low air pressure in the brake system (below 60psi).-Insufficient brake valve delivery pressure.-Excessive leakage with brakes applied.-Restricted tubing or hose.-Treadle travel restricted.-If remote mounted brake valve, check linkage.

3.) Brakes Release Too Slowly-Brakes need adjusting or lubricating.-Brake valve not returning to fully releasedposition.-Restricted tubing or hose.-Exhaust port of brake valve, quick release valve, orrelay valve restricted or plugged.-Faulty brake valve, quick release valve, or relayvalve.-If remote mounted brake valve, check linkage.

4.) Brakes Do Not Apply-No air pressure in brake system.-Restricted or broken tubing or hose.-Faulty brake valve.If remote mounted brake valve, check linkage.

5.) Brakes Do Not Release-Brake rigging binding.-Brake not in fully released position.-Faulty brake valve or relay valve.-Restricted or collapsed tubing or hose.-If remote mounted brake valve, check linkage.

6.) Brakes Grab or Erratic Brake-Grease on brake lining = reline brakes.-Faulty brake valve or relay valve.-Brake rigging binding.-No vehicle load = high brake pressure.

7.) Uneven Brakes-Brakes need adjusting, lubricating or relining.-Improper axle mounting.-Grease on brake lining - reline brakes.-Brake shoe return spring broken.-Brake drum out of round.-Brake chamber diaphragm failure.-Wrong brake lining.-Broken slack adjuster or foundation brake parts.

8.) Air Pressure Will Not Rise To Normal-Faulty air gauge (registering incorrectly).-Excessive valve or fitting leakage.-Governor out of adjustment.-Slipping compressor drive belt.-Faulty compressor.-Broken supply line.

9.) Air Pressure Rise To Normal Too Slowly

-Excessive valve or fitting leakage.-Excessive reservoir volume.-Clogged compressor air strainer.-Engine speed too slow.-Compressor discharge valve or inlet valvesleaking.-Compressor drive belt slipping or faulty drivecoupling.-Worn compressor.-Excessive carbon in compressor cylinder head ordischarge line.

10.) Air Pressure Rises Above Normal-Faulty air gauge ( registering incorrectly).-Governor out of adjustment.-Faulty governor and safety valve.-Restriction in line between governor andcompressor or restricted unloading valve.-Too much clearance at compressor unloadervalves or compressor unloading mechanism stuckin closed position.

11.) Air Pressure Drops Quickly WithEngine Stopped and Brakes Released-Leaking brake valve.-Leaking tubing or hoses.-Compressor discharge valves leaking.-Governor leaking.-Excessive leakage elsewhere in the air brake supplysystem.-Inadequate reservoir volume - high air demand.

12.) Air Pressure Drops Quickly WithEngine Stopped and Brakes Fully Applied-Leaking brake chamber, actuator, rotochamber orbrake cylinder.-Valve left open.-Leaking brake valve.-Leaking tubing or hose line.-Excessive water in reservoirs.-Inadequate reservoir volume.

13.) Compressor Knocks Continously or Intermittently

-Loose drive pulley.-Back lash in drive gears or drive coupling.-Worn or burnt out bearings.-Excessive carbon deposits in compressor cylinderhead.

14.) Safety Valve “Blows Off”-Safety valve out of adjustment.-Air pressure in the air brake system above normaldue to faulty unloader mechanism or faulty governor.

15.) Excessive Oil or Water in the Brake System

-Reservoirs not being drained oftern enough.-Compressor passing excessive oil.-Compressor air strainer restricted.-Excessive engine oil pressure.-Back pressure from engine crankcase.-Excessive oil (flooding) in compressor crankcase.

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Page 13QUALITY HEAVY DUTY PARTS

AIR BRAKE SYSTEM TROUBLESHOOTING1.) Before replacing any valve with a new or remanufactured valve, be sure to blow the air lines out eitherusing the vehicle’s own air supply or shop air. Dirt is the greatest cause of premature air valve failure.

2.) If pipe dope is used on fittings, use it sparingly. This can also get into the unit and cause a failure.

3.) When installing fittings into a remanufactured valve, do not over tighten or it will crack the casting.

4.) With the introduction of spring brakes, anti-compounding and 121 air brake systems, because a valve isleaking air out of its exhaust, does not mean the valve is at fault. If a spring brake is leaking from the thespring brake to the service brake side, that air will travel back up the service line and out the exhaust of thenext valve back. Before replacing a valve that has air leaking from its exhaust, disconnect the delivery linesfrom that valve to determine if air is being fed back from some other valve or unit.

TRAILERS** The air brake system of a trailer isentirely dependent upon the air brakesystem of the towing vehicle for its airsupply and control. Therefore, the air airbrake system of the towing vehicle mustbe in good condition; otherwise it will beimpossible to obtain a good brakeperformance on the trailer. Beforecondemning the air brake system on atrailer, always be sure the air brakesystem on the towing vehicle is function-ing properly. The following is based onon the assumption the tractor air brakesystem is functioning properly.

1.) Insufficient Brakes-Brakes need adjusting, lubricating or relining.-Tractor protection valve not in “normal” position.-Faulty relay emergency valve.-No trailer air supply - clogged emergency line.-Low air pressure in the brake system (below 80psi).-Brake valve delivery pressure in towing vehiclebelow normal.-Restricted tubing or hose.-Wrong size actuators.

2.) Brakes Apply Too Slowly-Brakes need adjusting or lubricating.-Low air pressure in the brake system (below 80psi).-Brake valve delivery pressure in towing vehiclebelow normal.-Restricted tubing, hose, or line filter.-Excessive leakage with brakes applied.-Faulty relay emergency valve.

3.) Brakes Release Too Slowly-Brakes need adjusting or lubricating.-Brake rigging binding.-Exhaust port of relay emergency valve restricted orplugged.-Restricted tubing or hose.

4.) Brakes Do Not Apply-Connecting hoses to trailer crossed.-Faulty relay emergency valve.-Tractor protection valve not functioning properlyor not in normal position (see operating instruc-tions).-No air pressure in air brake system.-Restricted tubing or hose.-Hoses between tractor and trailer not connected.

5.) Brakes Do Not Release-Connecting hoses to trailer crossed.-Brake valve on towing vehicle in applied position.-Brake rigging binding.-Relay emergency valve in emergency position.-Faulty relay emergency valve.-Restricted tubing or hose.-Tractor protection valve not functioning properlyor not placed in “normal” position.

6.) Brakes Grab-Grease on brake lining - reline brakes.-Brake rigging binding.-Faulty relay emergency valve.-Faulty brake valve on towing vehicle.-No trailer load.

7.) Uneven Brakes-Brakes need adjusting, lubricating or relining.-Grease on brake lining - reline brakes.-Brake shoe return spring broken.-Brake drum out of round.-Leaking brake chamber or actuator diaphragm.-Restricted tubing or hose.-Broken slack adjuster or foundation brake parts.

8.) Excessive Leakage With Brakes Released-Relay emergency valve or drain valve leaking.-Leaking tubing or hose.-Hose uncoupled or leaking hose coupling.

9.) Excessive Leakage With Brakes Fully Applied

-Faulty relay emergency valve.-Leaking brake chamber diaphragm.-Leaking tubing or hose.-Hose uncoupled or leaking hose coupling.

10.) Excessive Leakage with RelayEmergency Valve in Emergency Position-Faulty relay emergency valve.

11.) Excessive Oil and Water Present in the Air Brake System.-Reservoirs not drained often enough.

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QUALITY HEAVY DUTY PARTSPage 14

AIR BRAKE SYSTEM TROUBLESHOOTING

PROBLEM CAUSE REMEDY

1) Dryer is constantly cyclingor purging.

a. Excessive system leak.b. Defective governor.c. Defective one way valve between air dryer and wet tank.d. Kinked or plugged discharge line.

a. Repair air leak.b. Check governor for proper “cut-in,” “cut-out” pressure and excessive leakage. Repair or replace governor.c. Check to see if air is passing through check valve.d. Check to see if air passes through discharge line. Check for kinks, bends, excessive carbon deposits. Clean or replace discharge line.

2) Water and sludge appear in wet tank.

a. Plugged desiccant cartridge or filter.b. Improper length or material of discharge line.c. Restricted purge orfice.d. No purge cycle.e. Compressor passing excessive oil.

a. Replace dessicant cartridge filter.b. Use minimum of six-foot tubing for two- cylinder compressor; ten-foot for one cylinder compresssor. Flex hose can be substituted at a ratio of 1- 1/2’ of flex hose for each 1’ of metal.c. Clean orfice with small drill bit or wire.d. See cause and remedy for problem #5.e. Check for proper compressor installation. Replace compressor if necessary.

3) Safety valve on air dryer opens during operation.

a. Plugged or saturated desiccant cartridge or filter.b. Defective one way check valve.c. Restricted discharge line.

a. See remedy 2E, replace desiccant cartridge/ filter.b. Check to see if air is passing through check valve. Repair or replace check valve.c. Clean or replace air discharge line.

4) Constant leak of air from purge valve.

a. Purge control line connected to reservoir or exhaust port of governor.b. Inlet and outlet air connections reversed.c. Purge valve frozen open.d. Restricted discharge line.e. Faulty governor.

a. Purge control line must be connected to unloader port of governor.b. Compressor discharge line must be connected to dryer inlet port.c. Repair or replace thermostat/heater.d. Check to see if air passes through discharge line. Check for kinks, bends or excessive carbon deposits.e. Check governor for proper “cut-in,” “cut-out” pressure and excessive leakage. Repair or replace governor.

5) Air dryer does not purge or exhaust air.

a. Line between governor and dryer kinked, plugged, broken or frozen.b. Faulty heater or thermostat.c. Faulty purge valve.

a. Check to make sure air flows through purge control line when compressor is unloaded. Clean or replace purge control line.b. Repair or replace thermostat/heater.c. After determining air reaches purge valve, repair purge valve.

6) Slow air pressure build up. a. Restricted line.b. Plugged desiccant or filter.

a. Check to see if air passes through discharge line. Check for kinks, bends or excessive carbon deposits. Clean or replace discharge line.b. Replace desiccant cartridge.

7) Heater inoperative. a. Broken wire or bad connection.b. Blown fuse.c. Defective thermostat.

a. Repair or replace wiring to heater.b. Check fuse and replace if necessary.c. Repair or replace thermostat.

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